UHD After effects round tripping

Hi
Trying to send proreshq mov files 2160p from Avid to AE then back to Avid but I am getting color shifts. Same as source Avid export - render back to proresHQ in AE - AMA back to Avid. This is not a 709 vs RGB thing since there is only a slight change in gamma - it's more of a chroma saturation thing. Getting the same results on different machines (Mac trash cans). When I do the same round trip in 1080p, there is no shift. When I compare the original clip to the AE render in Premiere, I get the same shift, so it doesn't seem to be an Avid thing. AE seems to be adding metadata to the render that changes it slightly. I get a slightly different shift when I try it with a DNXHRX clip, but there is still a shift. Color management is set to none in AE. I have tried 8 bit and 16 bit project settings.
Anybody doing successful round trips in UHD in AE?
Thanks
Chris